Manufacture of caps for armor-piercing projectiles



ROBERT ABBOTT HADFIELD, OF WESTMIN STER, ALEXANDER GEORGE MOKENZIE JACK, 0F BRINCLIFFE, ISAAC BERNARD MILNE, OF TOTLEY, AND ESMOND MORSE, or SHEFFIELD, ENGLAND.

MANUFACTURE OF CAPS FOR ARMOR-JPIERCING PROJECTILES.

No Drawing.

To all whom it may concern: I

Be it known that we, Sir ROBERT ABBOTT HADFIELD, baronet, F. R. S., ALEXANDER GEORGE MCKENZIE JACK, ISAAC BERNARD MILNE, and EsMoNo MoRsE, subjects of the King of Great Britain and Ireland, residing,

respectively, at the city of Westminster,

England, rincliffe, in county of York, England, Totle in the county of Derby, England, and hefiield, in the county of York,

England, have invented Improvements in or range and therefore at comparatively low velocities, and particularly when striking obliquely at large angles, say of the order of about 20 and upward, without becoming broken up, or broken up to such an extent as to interfere with their subsequent desired.

tact with the plate at the moment of im-' pact, even when striking at a considerable angle. Such front end portion or head should be made of considerable hardness and toughness and be supported by a stiff rear portion so that when the cap is fitted to a projectile, it will, on impact against a hard faced armor plate, cause an initial disintegration of the surface of the plate by reason of the mass of hard metal in its front portion, together with the rigid support of the stiff and tough material in the rear of such hard portion.

In order to produce a cap possessing the Specification of Letters Patent. Pate t d 23 192,0

Application filed July 9, 1919. Serial No. 309,769.

special features or characteristicsabove" set forth, it is made of an alloy steel, for example of nickel chromium steel, of a composition that Will admit of its front portion bemg hardened to a high degree, and of the other required physical and mechanical characteristics being imparted to itby suitable heat treatment. To this end, it may for example be formed of nickel-chromium steel containing from about'.50 to .770 of carbon, from about 2 to 4% of nickel and from about 1.5 to 3% of chromium. The cap is formed to the required shape and dimensions,.as by casting or forging,-or casting and forging, and machining operations and, if desired, it may be annealed in the ordinary way or in any suitable way. The cap may be for .ex-

ample of ordinary conical shape with. a

rounded front end portion of such dimensions, for example of about one point three inches radius in the case of a cap for a 15 projectile, that when striking an arlnor plate, only a comparatively small area of such forward end of the cap will come into contact with and disintegrate theface of the plate, even when striking at a large angle, say at 20 or more, and so prepare the way for the pointed end portion of the projectile over which the cap is fitted, to suecessfully'attack the plate and enable the projectile to pass successfully therethrough. The front of the cap may be of conical shape if desired and in each case it may be flattened to some extent at its extreme front end over a small area. i

The can after being formed to the required hape is subjected to heat treatment inorder to harden and temper it in such a way as to impart to it different degrees of hardness varying sa from a ball hardness of from about 600 to 00 at the pointedfront end portion or zone through successive rearward zones of about 500, 400 and 300 ball hardness and so that the zones merge gradually one into the other and impart to the cap the required characterlstics hereinbefore mentioned. I

The degree of hardness corresponding to a ball hardness of 600 and above 1s hereinafter referred to for brevity and distincthat corresponding to 4:00 to 500 as Cball hardness, that corresponding to 300 to 400 as D ball hardness and that below 300 as E ball hardness.

Caps of the character above referred to have heretofore been made. For producing such a cap, the cap made of nickel chromium steel, in which the carbon may vary up to .6 to .7%, after being formed to the required shape, has had its front end portion according to some of the methods heretofore adopted, heated to a temperature of about 850 C. after which the cap was dipped while at this temperature in cold water to a zone depth that is to say, for part only of its axial length, so as to stiffen and harden the cap to the desired degree at different parts thereof, the cap thus treated possessing zones of decreasing ball hardness from its front end, where it has a ball hardness of from 500 to 600 and above, to the rear end portion where it has a ball hardness of from 300 to 200, the cap bein thuscomposed of zones of steel of A, B, of ball hardness.

In this way a cap can be produced having a dead hard front end portion and a stiffened or toughened rear end portion.

The present invention relates to improved methods of hardening and tempering caps of the kind hereinbefore referred to, whereby the special characteristics of hardness, stiffness and toughness now required, can be imparted to the caps in a better manner than heretofore and so that caps having the required characteristics can be produced in a regular or uniform and reliable manner.

For this purpose, a cap, which may advantageously be of nickel chromium' steel, such as hereinbefore referred to, after being formed to the desired shape and after having been subjected, it may be, to'a preliminary annealing or equivalent heat treatment, is subjected to the following improved heat treatment for hardening and tempering it.

Forhardening the cap it is first gradually and uniformly heated to a temperature, say

.of from about 820 to about 840 C., the

higher the hardening element or elements in the steel the lower the temperature used, the cap being finally heated to a practically uniform temperature throughout. The gradual heating of the cap ,may conveniently be effected in stages or steps in a gas fired furnace having a suitable contrivance.

for rotating the cap as it is being heated, to insure even heating to a high temperature. It is then quenched by immersing it in a suitable cooling medium to a certain depth and for a convenient time in such a way that by the action of the cooling medium upon the thicker portion of the cap together with or alternately by the action of the air upon the thinner portion, the whole material of the cap is rapidly cooled and so hard- (3 D, and E degrees ened. For instance, the heated cap is, while suitably suspended, for example in a ringlike holder, hardened all over by dipping it the cap, after the water has receded a certain distance, may be taken out of the wa ter, the cap having co oled to such an extent as to retain its hardness; Or the cap may be gradually lifted out of the water by means of a suitable appliance instead of lowering the water level.

.By the treatment described, notwithstanding the varying thickness of the metal com prising the cap from its base end to its forward end, the metal can be hardened throughout the whole mass thereof. Dur ing this hardening treatment the cap is or may be slowly rotated in the water in order to insure uniformity of hardening. The cap may also be hardened in oil or by other cooling medium, as for example an air blast, at suitably modified temperatures in order to produce the hardness required.

The rate at which the Water is run off, or

the cap lifted out of the water, can be varied to suit requirement. The rate of outflow of the water, or the rate at which the cap is lifted out of the water, is preferably such that when the cap is sufficiently hardened, it is taken out of the water while it is still. hot, but below a temperature of about 200 0., as at this temperature the hardness imparted to the cap will not be affected by the residual heat left in the cap. The cap after removal from the water, is cooled preferably in the air, for which purpose it may be placed on the floor of the shop in which the heat treatment is carried out.

Alternatively, the cap may be immersed in water, preferably running, to a definite depth, or series of definite depths, each for a certain time and then removed from the cooling medium. For example, a 150 lb. cap for a 13.5 inch shell would be immersed substantially to one half its overall length in running water for a period of 9 minutes.

The cap thus hardened throughout its mass is then tempered by heating its rear end portion to impart to the whole cap the requlred var ing degrees of A, B, C, D and E ball har ness. This tempering can be effected in various ways.

According to one. way of carrying out the tempering process, the rearward portion of the hardened cap is heated say to a temperature of the order of about 750 (1, for a nickel chromium steel such as hereinbefore referred to,.while the forward portion of the cap is kept cool or comparatively cool, as for instance by exposing itto the air, the heating being continued for a sufiicient time, say for example for about fifteen to twenty minutes in the case of a cap for a 13.5" armor piercing projectile, to reduce the hardness'of the cap to the required ball hardnesses while leaving the-portion of the cap infront of the point of the shell mainly of A and B ball hardness- For tempering a cap in the manner just described, the cap may advantageously be suspended in a holder base end downward,

I and immersed to a suitable depth or depths in a bath of molten metal, for example lead, or molten salts, at a temperature of, say for example, the order of about 750 0., and held there until the blue color temper line produced on the exposed surface of the cap reaches a predeterminedheight, varying for caps of different sizes and to suit diiferent requirements. The base end of the cap may advantageously be immersed toa depth of about 25% of the length of the cap in the molten lead and beheld in that position until the blue color temper line reaches a height of about 50% from the base end of the cap, which it will do in about fifteen minutes for a cap suitable for a 13.5" projectile and such as hereinbefore referred to. The cap is then removed from the lead bath, suspended point downward, as in a ring-like holder, and allowed to cool, preferably in the air.

Or the front end portion of the hardened cap, in an inverted position, may be immersed in cold water or other liquid while the other and upper rear portion of the cap is heated, as for example by the application thereto of an annular series of gas flames, to about the temperature mentioned, for a suitable time to temper it to the degree required.

The whole cap may then be allowed to cool in the air.

By the means described there can be ob tained a hardened and tem ered cap having successive zones of'A, B, d, D, and E ball hardness extending rearward from its point,

described, the reqpired varying volumes of steel of A, B, G, and E ball hardness and other desirable characteristics can be imv hereinbefore described can advantageously be applied to caps of different shapes and made of steel of various kinds.

What We claim is 1. A process for the manufacture of a cap for an armor piercing projectile from alloy steel capable of being hardened and tempered, said process consisting in heating the cap to a substantially uniform temperature and quenching the required length of it in a suitable cooling medium so that the whole of theca-p is rapidly cooled and hardened, then heating its rear end portion while its point is kept cool or comparatively cool, to temper the cap and finally cooling the cap. I

2. A process for the manufacture of a cap for an armor piercing projectile, said process consisting in heating a cap made of nickel chromium steel to a substantially uniform temperature and quenching the required length of it in water so that the whole of the cap is rapidly cooled and hardened, then heating its rear end portion while its point is kept substantially cool, to temper the cap in the required manner and finally cooling the cap. 3. In the process as claimed in claim 2. finally cooling the cap in air after heating it for tempering.

4:. In the process as claimed in claim 2, heating the cap to a temperature of the order of from about 820 to 840 C. preparatory to quenching it.

5. In the process as claimed in claim 1, hardening the cap by immersing it in a cooling liquid from its point to some desired extent of its length.

6. In the process as claimed in claim 1, hardening'the cap all over by immersing it, point downward, in a cooling liquid nearly to its base and then gradually reducing the influence of the cooling medium thereon by varying the level of the liquid relatively to the cap.

7. In the process as claimed in claim 1, hardening the cap all over by immersing it, point downward, in a cooling llquid nearly to its base end and then gradually withdrawing it from the influence of the cooling liquid by running oif the liquid.

8. In the process as claimed in claim 1, hardening a cap made of nickel chromium steel of substantially the composition herein set forth, by heating it-to a temperature of theorder of about 820 to 840 C. and immersing it point downward in water nearly to its base and then graduallywithdrawing it from the cooling influence of the water.

9. A process of tempering a cap that has been hardened all over, said process consisting in vheating the rear end portion of the cap, for a suitable time,- to a suitable tempering temperature while its front end portion is exposed to a cooling medium and afterward slowly cooling the said rear end portion of the cap.

10. In the process as claimed in claim 1, tempering a cap that has been hardened, by supporting the cap point upward and immersing a suitable length of its rear end por tion in molten material at a suitable temperature.

11. In the process as claimed in claim 1 tempering a cap that has been hardened, by supporting the cap point upward and immersing a suitable length of its rear end portion in molten metal at a suitable temperature.

12. In the process as claimed in claim 1,

tempering a cap that has been hardened, by inserting the cap base end downward for approximately 25% of its overall length, in a bath of molten lead at a suitable tempera ture while exposing its front end portion to a cooling medium and removing the cap from the molten bath when the hardness of each portion of the whole cap has been reduced to the requisite degree.

13. In the process as claimed in claim 1, tempering a cap that has been hardened, by inserting the cap base end downward for approximately 25% of its overall length in a bath of molten lead at a suitable temperature, while exposing its front end portion to the air, removing the cap from the molten bath' when the hardness of each portion of the whole cap has been reduced to the requisite degree and cooling the cap in air.

Signed at London, England, this fourth day of June, 1919.

RUBERT ABBOTT HADFIELD.

ALEXANDER GEORGE .WlchENZlE JACK. lSAAC BERNARD MIILNE. .ESlVlUND MORSE. 

